1. Field of the Invention
The present invention relates to improvement of a probe for use with a probe card for testing internal connection of an IC wafer.
2. Description of the Related Art
Probe cards are used to test internal connection, characteristics, or performance of IC wafers and so on. A typical probe card is provided with a probe corresponding to an electrode pad formed on each chip on an IC wafer. By pressing the probe onto the electrode pad, tests of electric connection of the pad, such as an open test and a short test, can be performed.
Meanwhile, as memory devices have come to have larger capacities within smaller packages, the interval of electrode pads formed on an IC wafer has grown smaller, and now is commonly about 40 xcexcm. Accordingly, electrode pads have also grown smaller.
To cope with this reduction of intervals between electrode pads, an interval between probes of a probe card for testing connection of an electrode pad must also be reduced. In other words, the diameter of a probe must be made smaller. FIGS. 6 and 7 show a shape of a probe of a conventional probe card, which has been devised to meet such a demand for a smaller interval.
As shown in these drawings, a probe 10 for a probe card is formed having a constant diameter, perhaps 150 xcexcm, so as to be resistive to the pressure with which the probe 10 is pressed onto an electrode pad 11. The tip end 14 of the probe, or a part to be brought into contact with a test object, is formed tapered, or having a taper 12, corresponding to the thickness of the probe. A plurality of such probes 10 are attached to a probe card, and used in a test on electric connection of a plurality of electrode pads formed on a chip.
It is desirable that a probe, which is brought into a contact with a test body to test electrical connections based on conductivity be manufactured of a highly conductive, low contact resistive, and less deformable material due to repeatedly applied stresses. When a probe is pressed directly onto a test body to apply a force thereto, metal flakes may be caused due to friction sliding. Metal flakes are quite harmful and impede accurate measurement.
Meanwhile, a probe made of a material much superior in low contact resistance and high conductivity may generally be weak in strength and thus exhibit inferior restoration to its original shape against repeated stresses when being pressed onto a test body. To meet the above four conditions of high conductivity, low contact resistance, anti-abrasion, and relatively high strength, materials such as rhodium, iridium, and so on are used for probes, even though they are expensive.
A probe is repeatedly used more than hundred thousand times or even million times in an operation to test characteristics of test bodies, and specifically moved, while being in pressured contact with a test body, between the probe and a test body in a test. Therefore, a probe must restore to its original shape after every test operation, even when severe stress is applied to the probe. In this view, a highly elastic material is used for a probe, though such material generally has high contact resistance. Therefore, a larger stress is constantly applied to a conventional probe whereby a certain level of constant contact resistance is retained. This, however, may likely cause deformation or destruction of a probe in an attempt to reduce reducing the probe diameter in order to cope with the need for a smaller pitch.
In addition, as a probe is made of a material harder than that of the object, such as an electrode pad, to be contacted by the probe, metal flakes may be caused during repetitive test operations. Metal flakes may adhere to the contact surface of a probe, and change a contact resistance value. In order to avoid this problem, the tip end of the probe may be machined or ground, upon necessity.
However, as the tip end of a probe is formed tapered, the diameter of the tip end becomes gradually larger as the tip end is being ground. When the diameter is thus changed, the pressure with which and a contact area via which a contact portion of the probe is pressed onto a test body in a test is also changed accordingly. This hinders testing under stable conditions.
Note that Japanese Patent Application Laid-open No. Hei 10-319037 (laid-open date Dec. 4, 1998) is incorporated herein by reference as related art of the present invention.
The present invention has been conceived to overcome the above problems and aims to provide a probe for use with a probe card with improved resistance to repeatedly applied stresses, allowing testing under stable condition over a long term.
According to the present invention, a covering layer is made of either a first metal which is softened through solution treatment at 1000xc2x0 C. to 1200xc2x0 C., and then hardened in aging treatment at 400xc2x0 C. to 500xc2x0 C., or a second metal which is softened through annealing and then significantly hardened through working. A probe shaft, supported by the covering layer made of either material described above for reinforcement, is more resistive to stresses repeatedly applied thereto.
Preferably, a probe of a probe card according to the present invention may have a contact portion with a length at least 10 xcexcm, and a constant diameter.
As a contact portion has a predetermined length and a constant diameter, the diameter of a tip end of the contact portion will not be changed, in particular, larger, even when the tip end is machined or ground.
Preferably, the probe shaft of a probe of a probe card according to the present invention may be made any of PALINEY (trademark) (an alloy essentially consisting of Au (10 wt %), Pt (10 wt %), Pd (35 wt %), Ag (30 wt %), Cu, Zn), beryllium copper (Bexe2x80x94Cu), a material from platinum group elements, gold, and gold silicon.
Preferably, the probe shaft of a probe of a probe card according to the present invention may have a multi-layered structure, with each layer being composed of any of PALINEY (an alloy essentially consisting of Au (10 wt %), Pt (10 wt %), Pd (35 wt %), Ag (30 wt %), Cu, Zn), beryllium copper (Bexe2x80x94Cu), a material from platinum group elements, gold, and gold silicon, and to be combined with other layer or layers.
According to the present invention, there is provided a method for manufacturing a probe of a probe card. The probe has a multi-layered structure, including a probe shaft made of conductive metal, of which a contact portion provided at the tip end thereof is brought into contact with a test body to measure electric connection of the test body, and a covering layer including at least one layer formed around an external circumferential surface of the probe shaft. Preferably, the method comprises the steps of: providing a conductive metal bar to be formed into the probe shaft, in a metal cylinder to be formed into a covering layer; softening the conductive bar metal and the metal cylinder in solution treatment or annealing; and stretching the conductive bar metal and the metal cylinder in a softened state, using a coaxial wire drawing method, whereby a probe having a multi-layered structure is formed.
According to the present invention, an inexpensive multi-layered probe of a probe card having high resistance to repeatedly applied stresses and low pressured stable contact resistance, and which does not readily chip metal can be readily manufactured.